The goals of this study are to examine varicella-zoster virus (VZV) replication and the development of immunity in normal subjects with natural infection and to determine the immune factors important in resistance to re-infection among naturally immune subjects as background for the evaluation of live VZV vaccine. Antibody responses, including IgG, IgM and IgA, will be measured by solid phase radioimmunoassay. Cellular immunity will be assessed by in vitro lymphocyte transformation to VZV antigen to detect VZV sensitized T lymphocytes. These assays will be used to determine whether the re-exposure of immune subjects to exogenous VZV is associated with an anamnestic immune response. The effect of transplacentally acquired antibody upon the outcome of exposure to varicella will be studied to determine whether infection is prevented or whether subclinical infection occurs. IgM production and the development of lymphocyte transformation will be used as markers of asymptomatic infection. VZV replication in sites other than skin, including the nasopharnyx and circulating blood cells, will be investigated during primary varicella. Local immunity, measured by IgA antibody and interferon production in nasopharyngeal secretions will be assessed during primary infection and with re-exposure of immune subjects to the virus.